With the development semiconductor technology, critical dimensions (CDs) of semiconductor devices become smaller and smaller, the integration degree of IC chips have become more sophisticated, and more stringent requirements are made for the semiconductor manufacturing processes. It is therefore desirable to reduce errors often occurred in every step during the semiconductor processes and to reduce device failure.
Photolithography process plays an important role in the semiconductor manufacturing processes. In a standard CMOS process, dozens of photolithography processes are needed. The photolithography processes, however, may be affected by resolution of photolithographic machine and alignment accuracy. Errors are often occurred in the photolithography processes.
In a photolithography process, scanning electron microscope (SEM) may be used to measure patterns formed in the substrate, by an etching process using a photoresist layer or other film layer as an etch mask. In an SEM measurement, an electron gun emits electron beams. The electron beams are then focused on surface of the pattern. High-energy electron beam thus interacts with the material of the pattern. A secondary electron collection generated on the pattern may be amplified and then sent to the gate of a picture tube to form various image features for observation.
However, it is not efficient when using an SME imaging measurement method for measuring a mask pattern.